Circuit arrangement for imitating the touch of musical instruments with percussion

ABSTRACT

A circuit for controlling the amplitude of an audio oscillator in an electronic musical instrument in response to the intensity with which a key is depressed. A voltage produced by a coil in response to the movement of a magnet attached to the key charges and output capacitor through a resistor and a diode. A reverse bias of a predetermined level impressed on the diode insures that the time during which a charging voltage is impressed on the capacitor is approximately equal for all levels of voltage produced by the coil.

United States Patent 11113,553,337

[7 2] Inventors Popko Reinder Dijksterhuis. deceased, [50] Field ofSearch 84/ l .01 late of Bilthoven, 1.13, 1.26, 1.27; 307/246, 256, 259Casper Antonius l-lenricus Mulkens, Administrator, Eindhoven,Netherlands [5 6] References Clted [21] Appl. No. 719.832 UNITED STATESPATENTS 1 Filed P 1968 2,841,043 7/1958 Schreiber 84/1. 1 3

[ 1 Patented 5, 0 3,239,693 3/1966 Janning 307/259 [73] Assignee U. S.Philips Corporation 3,248,470 4/1966 Markowitz et al. 84/1. 13X NewYork, 3,336,484 8/1967 Ovshinsky 307/256X a corporation of Delaware. bymesne assignment Primary Examiner-Herman Karl Saalbach [32] PriorityApr. 8, 1967 Assistant Examiner-T. Vezeau [3 3] NetherlandsAttorneyFrank R. Trifari [54] CIRCUIT ARRANGEMENT FOR IMITATING THETOUCH OF MUSICAL INSTRUMENTS WITH PERCUSSION 5 Claims, 6 Drawing Figs.

[52] U.S. Cl 84/1.l3, 84/1.26 [51] Int. Cl GlOh 1/02 ABSTRACT: A circuitfor controlling the amplitude of an audio oscillator in an electronicmusical instrument in response to the intensity with which a key isdepressed. A voltage produced .by a coil in response to the movement ofa magnet attached to the key charges and output capacitor through aresistor and a diode. A reverse bias of a predetermined level impressedon the diode insures that the time during which a charging voltage isimpressed on the capacitor is approximately equal for all levels ofvoltage produced by the coil.

PATENTED JAN 5 I97! SHEET 1 BF 2 INVENTOR. POPKO REINDERDlJKSTERHUlS,DEC-EASED, BY CASPER ANTONIUS HENRICUSMULKENS,ADM!NISTRATOR AGE I PATENTED JAN 5197! SHEET 2 BF 2 FEESINVENTOR. POPKO REINDER DIJKSTERHUIS, DECEASED, BY CASPER ANTONIUSHENRICUS MULKENS,ADMINISTRATOR AG NT produces a voltage having a valuewhich depends upon the intensity of thetouch, which voltage thendecreases again to zero. V

In such an instrument, it is desirable that the buildup time of the tonefor various. intensities of touch should be as constant as possible oratleast should not exceed a given value with a soft touch, sincethecharacter of theinstrument is then lost.

For example, with a'pia no, the builduptime never exceeds milliseconds;The term buildup time is to be understood'to mean the time in which thetonerises from zero to its-maximum amplitude. lri the known instrument,this is the time in which the capacitor is charged by a current of acoil in which,

i when an associated key'is touched, an e.m.f. is produced by amagnetconnected to this key. v Since the-initial and final positions ofthis magnet are always the same, the flux variation db 2is constant andthe voltage produced is in inverse proportion to the duration 1 of thetouch and hence in direct proportion to the intensity of the touch.However, it is desirable for this buildup time to be constant or atleast to vary to a smaller extent than the duration of the touch.

According tothe invention, this is achieved by biasing'the'rectifying'element'so that only part of the touching pulse is Withthesofiest touch, which is the touch producing sound vibrations which arejust audible, the bias voltage has a considerably greater influence thanwith the strongest touch,

since the amplitude of the voltagepulses produced by the touch isproportional to the rate at which the magnetic field in the coil isvaried, while the bias voltage remains constant.

.Thus, the part of the voltage pulse produced which ispassed by therectifier has a duration equalto only part of the half period of thisvoltage pulse, whereas with'thestrongest touch substantially the wholevoltage pulsev is passed and hence has a duration of substantially-ahalf period.

With a piano, for example, the ratio between the minimum intensity oftouch, i.e. the intensity of touch with which the hammer just reachesthe string, and the maximum intensity of touch is in practiceapproximately 1 100. This ratio cor- .responds to a ratio between thetouching times of approximately l0 l and'between the amplitudes of thestring of approximately l 10 so that the desired ratio between thecapacitor voltages is also approximately 1 10.

In a preferred embodiment of a-musical instrument according to theinvention, the bias voltage exceeds half the peak value of the voltagepulse produced with the softest touch. In this case, the ratio betweenthe buildup times is at least 1.5

' times and with a triangular voltage.- pulse, which is usual inpractice, even 2 times more favorable than without the application of abias voltage.

It will be appreciated that this bias voltage can be produced in anyknown manner, while in certain cases the threshold voltage of therectifying element may advantageously be used. Alternatively, therectifying element may be biased by means of the series-combination of adirect voltage source and a resistance which is connected in parallelwith the rectifying element, or the direct voltage may be connected inseries with the whole charging circuit.

When according to a further embodiment a resistance is connected in thecircuit in series with the rectifying element, it is achieved that withthe softest touch, the capacitor is charged in a time t, which occupiesa smaller part of the duration 1', of the smallest touching pulseyth'atis the time t of the duration 1, of the largest touching pulse with thestrongest touch, so that the ratio between the buildup times of the tonecorresponding to t, and t becomes even more favorable. The

resistance is then chosen to be high with respect to the resistance ofthe diode.

Thus, it is also achieved that the ratio between the capacitor to theinvention, the rectifying element is connected in series with a memberthe resistance of which increases with increasing current in thestarting-current range of the said rectifying element.

This is advantageous in those cases in which the resistance in thecircuit is low with respect to the resistance of the diode and in whichmoreover the rectifying element is operative only in itsstarting-current range with a soft touch. The step described aboveensures that the resistance in the circuit remains more constant so thatthe phase shift between the chargingcurrents of the capacitor-and thepulsatory voltage remains small.

As far as the ratio between the capacitor voltages, which had becomeunduly large owing to the application of the bias voltage, has not yetor not sufficiently been reduced to the correct value by the stepdescribed above, this may be effected in another embodiment ofa musicalinstrument according to the invention by connecting a biased overflowdiode in parallel with the coil.

The invention will now be described with reference to the followingFIGS. of which:

FIG. 1 tion;

touch;

FIG. 3 shows a circuit arrangement including a member the resistance ofwhich increases with increasing current;

FIG. 4 shows in a graph the effect of this step;

, FIG. 5 shows a circuit arrangement including an overflow diode; and

FIG. 6 shows the voltage variation V of the coil as a function of theintensity of touch.

FIG. 1 illustrates that a magnet 2 coupled with a key 1 varies themagnetic field in the inductance L when the key is depressed. Thevoltage induced in the inductance L charges a capacitor C through aresistor R- and a diode D serving as rectifying element. The diode D isbiased with a voltage E supplied by a battery B.

FIG, 2 illustrates the variation of the capacitor voltage as a functionof time with two different intensities of touch. The soft touch isassociated with the induced voltage E The half sine E has a duration 1'Without the application of a bias voltage, thecapacitor voltage wouldvary in accordance with the line V It thus appears that the buildup timet, slightly exceeds h 1 It is assumed that the resistance in the circuitis only low with respect to the impedance of the capacitor for thisfrequency. With a touch which is three times stronger than the softesttouch and the associated voltage pulse of which is denoted by E thevoltage across the capacitor becomes V, As is apparent from the FIG.,the ratio between the times 1', and 7 is substantially equal to thatbetween the times t, and t When according to the invention the diode Dis biased with a voltage E which preferably exceeds half the peak valueof E and in the case of the pulse in the form of a half sine shown 0.7times this value, the duration r, of the voltage pulse IE is reduced to1' and the duration 7 of the voltage pulse E, to 1 In case the voltagepulse is triangular, a bias voltage of 0.5 results in a reduction of thebuildup time by 0.5. It will be appreciated that the reduction of thesetimes is larger as the voltage pulse produced is smaller with respect tothe bias voltage E. The buildup times t;, and t, of the voltages V,,'and V across the capacitor also decrease, bjut t3 to a larger extentthan t,,, so that the ratio between the buildup times, which without theapplication of a bias voltage was approximately equal to 3 shows acircuit arrangement according to the inven- FIG. 2 shows the variationof thecapacitor voltage and'of Q the e.m.f. produced in the coil withdifferent intensities of is now only 1.5 or smaller. However, due tothis step, the ratio between V and V has become larger than 3, which maybe undesirable. This disadvantage can be mitigated by connecting aresistor in series with therectifying element. At higher frequencies andhence with stronger touches, the phase'shift between the capacitorvoltage and the voltage pulse induced in the coil will then increase,while with strong touches the capacitor voltage V will be low withrespect to the voltages induced, so that the ratios between'thesevoltages more closely approximate the ratios between the intensities oftouch. Moreover, with a stronger touch, the buildup time t of .the new.capacitor voltage V thus exceeds whilethe buildup ytime I, of thecapacitor voltage V,," associated withthe soft touch hardly varies witha suitable proportioning of the resistor R and the capacitor C, so thatthe ratio between the bui]- I dup times t, and I is even furtherreduced.

If the peak value of the voltage E induced with the softest touchexceeds the bias voltage E by such a small amount that fect iscompensated for by connecting in series with the diode a member X (cf.FIG. 3) the resistance of whichincreases with increasing current in thestarting-current range of the diode D so that the overall resistanceofthe circuit varies less strongly. Such a member may. comprise aresistorhaving a positive temperature coefficient, a tunnel diode ofwhich the part having a vnegative resistance is .used, a. diode thecurrent of which 4' remains constant in a wide voltage range, and so on.The result is shown by the dotted line in FIG. 4.

For the sake of clarity, F IGS. 2 and 4 show only the case in which theintensity of touch varies only by a factor 3', but it will beappreciated that what has been said as to a touch thrice stronger thanthe softest touch applies to an even greater extent to a touch intensityratio of l l0.

The intensity of touch is here always correlated to the rate at whichthe magnet is pushed into the coil; the amplitude of the voltage pulseis then directly proportional thereto.

. As is apparent from FIGS. 2 and 4, the output voltage ratio exceeds 13.

This may be compensated for by providing an overflow diode biased withthe voltage E, (cf. FIG. 5). The effect of this diode is shown in FIG.6, in which the voltage V is plotted on the ordinate and the intensityof touch B on the abscissa. V, in-

dicates the variation of the voltage across the coil. This variation islinear. Due to the application of the bias voltage 8, the

capacitor voltage is reduced by thisval ueat. an ,inher ity of touchsothat at a ratio between the intensities, example, I

' Like inthe known instrument,"thecapacitorvoltageis'sup plied to acontrolmember which"passes,tlie-oscillationscnly .when'the capacitor isin the chargedstate,

3, the. ratio between the: .c'apacit now become I': 7, as appears fromievariation to the capaciof which decreases withincreas ratio and hencethe dynamic range rsfbrdtigh bac rect value, as shown by the curveOrv... A

The bias voltage of thezchargin'g ode D and the bias voltage'oftheoverflow rode by E The capacitor may also compris'e a s'eiies-combination "of two capacitors-and a resistor;may.be onnected inparallel with one of them. Moreover,=the capacitor-maybe connected inparallel with a discharge circuit whichensures that the tone v willdecaycorrectly.

Iclaim: .T I l. A control circuit providinganoscillator in an electronicmusical instrument-with am output voltage having an-amr plitudecorresponding to theavelocitywithwhich movably .mounted key isdepressed, comprising a magnet, a coil, means for providing relativemotion between said .coil and said mag;

net in response to movement ofsaid key, whereby a voltage is Q inducedin said coil corresponding to the velocity of said ltey i a capacitor, adiode, means for connecting said capacitor-a said diode'in series,circuit means for connecting said series. connected diode and capacitoracross said coil, whereby said .capacitor is charged in response to thevoltage acrossfsaidcoil,

andmeans for biasing the diode with a voltage less than the lowest peakvoltage produced in the coil as a result of the softest touch on thekey.

2. An electronic musical instrument as claimed in claim 1, wherein thebias voltage exceedshalf the peak value of the voltagepulse producedwith the softest touch.

r 3. An electronic musical instrument as claimed in claim 1 furthercomprising a resistor-connected inseries with the

1. A control circuit providing an oscillator in an electronic musicalinstrument with an output voltage having an amplitude corresponding tothe velocity with which movably mounted key is depressed, comprising amagnet, a coil, means for providing relative motion between said coiland said magnet in response to movement of said key, whereby a voltageis induced in said coil corresponding to the velocity of said key, acapacitor, a diode, means for connecting said capacitor and said diodein series, circuit means for connecting said series connected diode andcapacitor across said coil, whereby said capacitor is charged inresponse to the voltage across said coil, and means for biasing thediode with a voltage less than the lowest peak voltage produced in thecoil as a result of the softest touch on the key.
 2. An electronicmusical instrument as claimed in claim 1, wherein the bias voltageexceeds half the peak value of the voltage pulse produced with thesoftest touch.
 3. An electronic musical instrument as claimed in claim 1further comprising a resistor connected in series with the rectifyingelement.
 4. An electronic musical instrument as claimed in claim 1,further comprising a member connected in series with the rectifyingelement, wherein the member has an increasing resistance in response toincreasing current in the starting-current range of the rectifyingelement.
 5. An electronic musical instrument as claimed in claim 4further comprising a biased overflow diode connected in parallel withthe coil.